1. Field of the Invention
The invention relates to the air induction and exhaust processes of piston driven internal combustion engines which operate singularly as 2-stroke systems or as 4-stroke systems and to dual-cycle engines having the capability of alternately operating in either mode.
2. Description of Prior Art
The use of exhaust gas ejector systems in cylinder side-port manifolding circuits of the reciprocating piston engine is taught in the cross-referenced U.S. Pat. Nos. 4108119, 4248199 and 4312313. The use of exhaust gas ejector systems was extended to application in the cylinder head manifolding in cross referenced U.S. Pat. No. 5154141. This latter application provided the necessary mechanical facility for dual-cycle engine operation. The present invention utilizes many of the features of the cross-referenced patents in a unique manner which provides new and useful improvements in the design of the dual-cycle engine.
The invention comprises the induction and exhaust manifolding of a piston driven engine having an L-head valve arrangement. This type of engine configuration was most
popular in the so-called flat-heat designs which predominated the automotive engine market until about 1950. Although the present invention is not limited to the use of the L-head configuration it does provide the simplest means of combining the upper cylinder head manifolding with the lower cylinder side-port manifolding and thus reduces the number of manufactured components required.
In the design of most standard engine systems two poppet valves are employed at each engine cylinder. In order to increase engine power by increasing the volumetric efficiency of the system, and thus bring about the reduction of engine size, todays high performance engines now employ as many as 4 valves per engine cylinder. In the present invention only one valve is used per engine cylinder thus decreasing the number of manufactured parts required in the valve-train design. The number of valve-train components is further reduced in the present L-head configuration eliminating the need for rocker arms, push rods, overhead lubrication, valve cover and gaskets. This feature of the design reduces the amount of engine noise, and provides a lighter weight engine having a smaller envelope and most important it is less expensive to manufacture.
In the dual-cycle engine design it is desirable to increase the ejector air-chest manifold pressures in order to assure a positive differential pressure across the ejector diffuser in order to maintain a pulsating unidirectional flow through it. This constant flow of air through the diffusers into the exhaust manifold eliminates the need for a waste-gate necessary to prevent over pressurization.
Boost pressure to the air chest is also beneficial to efficient high speed sequencing through the ejector nozzle which must function as a bidirectional flow component. The rapid flow reversal within the ejector nozzle is most efficiently accomplished when air-chest pressures are high.
The preferred method of obtaining boost pressure is by mechanical or electrically driven superchargers.
Because of the high exhaust system back-pressures associated with the operation of turbochargers this method of obtaining boost pressure is less effective in dual-cycle engine design. However in some configurations of the cross-referenced patents good performance has been achieved using the upper exhaust gas manifold to drive the turbine and the blower to pressurize the lower cylinder side-port ejector air-chest.
When boost pressure is not applied, flow within the air-chest depends principally on the efficiency of the momentum exchange between the exhaust gas stream from the ejector nozzle and the air at the inlet of the ejector diffuser. Additional flow is obtained by the negative pressure phase within the engine cylinder during the exhaust blowdown.
The high ratio of surface to flow area within the annular opening of the poppet valve results in higher frictional losses than through other types of restrictive openings having the same flow area. In dual-cycle engine design this situation can be further aggravated by the additional restriction of flow in the ejector nozzle mounted in the cavity directly below the valve. Because only one valve is operating within the cylinder clearance volume valve over-lap is not a problem. Therefore the poppet valve is raised higher off its seat than would be practical in the design of engines having a plurality of such valves in each cylinder and thus the general problem of restrictive flow losses in this area is alleviated. Flow restriction at the ejector nozzle inlet in the cavity below the poppet valve must be designed sufficiently high in order to create a critical pressure ratio across the ejector nozzle promoting sonic flow at the nozzle inlet which is slightly accelerated in the nozzles conical section thus increasing the momentum exchange of the exhaust gas stream with the air stream in the air-chest.
The continuous flow of the supercharged air in the air-chest through the ejector diffuser helps to center the flow of the impacting exhaust stream in front of the diffuser inlet and facilitate its passage through the diffuser into the exhaust gas manifold Unlike the other types of poppet valve manifolding it is desirable to keep the volume of the cavity below the valve as small as possible which hardens the system by decreasing the volume available for compressibility and thus quickens the flow reversal in the nozzle during the subsequent induction reducing the cycle lag permitting the system to function more effectively while operating in the 2-stroke mode at higher engine speeds.
Because the inlet and outlet pressures of the upper and lower cylinder ejector diffusers operate at essentially the same pressure in the present invention the control of the engine is simplified over that of previous designs in which the upper and lower manifolds were controlled separately.